Phenol is an important product in the chemical industry and is useful in, for example, the production of phenolic resins, bisphenol A, ε-caprolactam, adipic acid, and plasticizers.
Currently, the most common route for the production of phenol is the Hock process. This is a three-step process in which the first step involves alkylation of benzene with propylene to produce cumene, followed by oxidation of the cumene to the corresponding hydroperoxide and then cleavage of the hydroperoxide to produce equimolar amounts of phenol and acetone. However, the world demand for phenol is growing more rapidly than that for acetone. In addition, the cost of propylene is likely to increase, due to a developing shortage of propylene.
Thus, a process that uses higher alkenes instead of propylene as feed and coproduces higher ketones, such as cyclohexanone, rather than acetone may be an attractive alternative route to the production of phenols. For example, there is a growing market for cyclohexanone, which is used as an industrial solvent, as an activator in oxidation reactions and in the production of adipic acid, cyclohexanone resins, cyclohexanone oxime, caprolactam and nylon 6.
It is known from U.S. Pat. No. 5,053,571 that cyclohexylbenzene can be produced by contacting benzene with hydrogen in the presence of a catalyst comprising ruthenium and nickel supported on zeolite beta and that the resultant cyclohexylbenzene can be processed in two steps to cyclohexanone and phenol. The hydroalkylation reaction is carried out at a liquid hourly space velocity (LHSV) ranging from 1 to 100, a reaction pressure ranging from 100 to 1000 kPa, a hydrogen feed rate ranging from 0.2 to 6 mole per mole of feedstock per hour, and a reaction temperature ranging from 100 to 300° C.
In addition, U.S. Pat. No. 5,146,024 discloses that benzene can be reacted with hydrogen in the presence of carbon monoxide and a palladium-containing zeolite X or Y to produce cyclohexylbenzene, which can then be converted in high yield to phenol and cyclohexanone by autooxidation with subsequent acid treatment. The hydroalkylation reaction is carried out at a liquid hourly space velocity (LHSV) of the benzene feed of about 1 to about 100 hr−1, a total reaction pressure of about 345 to about 10,350 kPa, a molar ratio of H2 to benzene of about 0.1:1 to about 10:1, a molar ratio of carbon monoxide to H2 of about 0.01:1 to about 0.3:1, and a temperature of about 100 to about 250° C.
Further, U.S. Pat. No. 6,037,513 discloses that cyclohexylbenzene can be produced by contacting benzene with hydrogen in the presence of a bifunctional catalyst comprising a molecular sieve of the MCM-22 family and at least one hydrogenation metal selected from palladium, ruthenium, nickel, cobalt and mixtures thereof. The catalyst may also contain a binder and/or matrix and in the Examples the catalyst is produced by impregnating an extrudate of the MCM-22 family molecular sieve and an alumina binder with an aqueous solution of a salt of the hydrogenation metal using incipient wetness impregnation. The '513 patent also discloses that the resultant cyclohexylbenzene can be oxidized to the corresponding hydroperoxide and the peroxide decomposed to the desired phenol and cyclohexanone.
In our co-pending U.S. Patent Application Ser. No. 60/964,874, filed Aug. 15, 2007, we have described a process for producing cyclohexylbenzene, the process comprising contacting benzene and hydrogen with a catalyst under hydroalkylation conditions to produce an effluent containing cyclohexylbenzene, the catalyst comprising a composite of a molecular sieve, an inorganic oxide different from said molecular sieve and at least one hydrogenation metal, wherein at least 50 wt % of said hydrogenation metal is supported on the inorganic oxide. By providing at least the majority of the hydrogenation metal on the inorganic oxide support rather than the molecular sieve, it is found that the activity of the catalyst and its selectivity to cyclohexylbenzene and dicyclohexylbenzene are increased.
In the Example disclosed in U.S. Patent Application Ser. No. 60/964,874, the inorganic oxide employed as the support for the hydrogenation metal was CATALOX SBa alumina, which has an average particle size of about 45 μm (microns). According to the present invention, it has now been found that the benzene hydroalkylation activity of a bifunctional catalyst, in which some or all of the hydrogenation metal is supported on an inorganic oxide separate from the molecular sieve, can be enhanced if the inorganic oxide is selected so as to have an average particle size less than 40 μm (microns). Moreover the increase in activity is obtained without significant loss in the selectivity of the catalyst to cyclohexylbenzene and dicyclohexylbenzene, which is desirable since any dicyclohexylbenzene can be readily transalkylated with additional benzene to produce further cyclohexylbenzene product.